1. Field of the Invention
The invention relates in general to a method of erasing an erasable disc, and more particularly to a method of erasing a DVD-RW disc without continuously detecting a LPP (Land Pre-Pit) data block.
2. Description of the Related Art
Because the DVD disc can store a large amount of data, it is very suitable for the storage of the high quality video and audio data with a huge data amount. Furthermore, because of the mass production of the DVD optical drives, the recordable DVD disc and the erasable DVD disc have been gradually used by the consumer to backup the large amount of data.
According to the DVD-RW specification, LPP (Land Pre-Pit) data blocks are recorded between two adjacent helical tracks on the DVD-RW disc. The LPP data block represents the actual address on the track of the DVD-RW. The track length represented by each LPP data block corresponds to the data amount that can be recorded in one ECC (Error Correction Code) block. Thus, the data of each ECC block on the DVD-RW disc may correspond to the position specified by one LPP data block. An ECC block address is also recorded in the data of each ECC block, and the ECC block address is the same with LPP data block.
FIG. 1 is a flow chart showing a conventional optical drive for executing an erase operation in an erase mode. The method includes the following steps.
In step 10, a starting address and an ending address of the ECC blocks are obtained in the erase mode.
In step 20, a start erasing position is obtained by seeking a corresponding LPP data block on the DVD-RW disc according to the starting address of the ECC block.
In step 30, a laser beam with an erase power is provided at the start erasing position of the DVD-RW disc.
In step 40, an erase operation is executed, and the LPP data block at which the laser beam positioned is detected.
In step 50, it is judged that whether or not the LPP data block, at which the laser beam positioned, matches with the ending address of the ECC block, and the process jumps to step 40 if yes, or otherwise to step 60.
In step 60, the erase operation ends.
In the erase mode, the optical drive gets an erase instruction from a host. At this time, the optical drive obtains the starting address and the ending address of the ECC blocks according to the erase instruction. Next, the optical drive detects the correspondent LPP data block on the DVD-RW disc as the starting position, and drives the laser diode to provide an erase power (Pe) from the starting position to erase data on the tracks of the DVD-RW disc. While the optical drive is erasing the data on the tracks of the DVD-RW disc, the LPP data block has to be continuously detected so that whether or not the ending address of the ECC block has been reached can be obtained. When the LPP data block is assured to be the ending address of the ECC block, the erase operation ends.
However, the DVD-RW disc can be rewritten multiple times. After the DVD-RW disc has been rewritten or erased multiple times, the LPP data block on the DVD-RW disc cannot be easily detected. The optical drive has to continuously detect the LPP data block while executing the erase operation in the erase mode. If the optical drive cannot detect the LPP data block to determine the stop erasing position, the optical drive continues executing the erase operation on the tracks, thereby causing the data lost or the erase failure.
FIG. 2 is a schematic illustration showing a conventional laser diode drive circuit of an optical drive. Typically, multiple current paths are superimposed to drive the laser diode. In the laser diode drive circuit as shown in FIG. 2, Ib is a bias current, Ie is an erase current, and Iw is a write current. The current value of each current path may be set individually, and a control switch (Sb, Se, Sw) is disposed on each current path to control the on and off states of the current.
FIGS. 3a and 3b respectively show a recording data signal and a write pulse signal in a write mode. As shown in FIG. 3a, if the recording data signal is 6T, the control chip set in the optical drive controls the laser diode to generate the write pulse signal of FIG. 3b. The switch Sb is on and the switches Se and Sw are off, such that the current Ib flows though the laser diode and the fundamental power of Pb is generated, as shown in zone 3. The switch Se is on and the switches Sw and Sb are off, such that the current Ie flows though the laser diode and the erase power Pe is generated, as shown in zone 2. The switches Se and Sw are on and the switch Sb is off, such that the currents Ie and Iw flow though the laser diode to generate the write power Pw, as shown in zone 1. That is, the control chip of the optical drive can control the switches Sb, Se and Sw to enable the laser diode drive circuit to generate the write pulse signal according to the recording data signal.